Liquid crystal display element

ABSTRACT

The present invention provides a liquid crystal display element that sufficiently improves the reliability and the optical characteristics, and can be driven by a low voltage. The liquid crystal display element of the present invention includes a pair of substrates; and a liquid crystal layer sealed between the substrates. The liquid crystal layer includes liquid crystal molecules having positive dielectric constant anisotropy, at least one of the substrates includes a pair of comb-shaped electrodes, at least one of the substrates includes a vertical alignment film in a display region on a face in contact with the liquid crystal layer, and the vertical alignment film is an inorganic alignment film made of an inorganic material.

TECHNICAL FIELD

The present invention relates to a liquid crystal display element. Morespecifically, the present invention relates to a liquid crystal displayelement suited for display modes in which light passing through a liquidcrystal layer is controlled by changing the alignment of liquid crystalmolecules in the liquid crystal layer into a horizontal bend alignmentby applying a voltage.

BACKGROUND ART

Liquid crystal display elements (hereafter, abbreviated as LCDs) arethin and light display devices with low electrical power consumption.They are used in various applications such as mobile phones, PDAs, carnavigation systems, PC monitors, televisions, and information displayssuch as guide boards in stations and outdoor notice boards.

In the current LCD display technology, the polarization of light passingthrough a liquid crystal layer is changed by controlling the alignmentof liquid crystal molecules by applying an electric field so that theamount of light passing through a polarizing plate is controlled. Thedisplay performance of LCDs depends on the alignment of liquid crystalmolecules under application of a voltage and the intensity and directionof an applied electric field. The display mode of LCDs is categorizedinto various groups based on the alignment of liquid crystal moleculesin a voltage free state, and the direction of an applied electric field.For example, TN (Twisted Nematic) mode liquid crystal display elementsand OCB (Optically Compensated Bend) mode liquid crystal displayelements are known as liquid crystal display elements of verticalelectric field modes in which the liquid crystal alignment in thevoltage free state is horizontal to substrates. These elements implementhigh transmittance, high-speed response performance, and the like. MVA(Multi-Domain Vertical Alignment) mode liquid crystal display elementsare representatives of liquid crystal display elements of verticalelectric field modes in which the liquid crystal alignment is verticalto substrates in the voltage free state, and TBA (Transverse BendAlignment) mode liquid crystal display elements are representatives ofliquid crystal display elements of horizontal electric field modes inwhich the liquid crystal alignment is vertical to substrates in thevoltage free state. These elements exhibit high contrast performance.IPS (In-plane Switching) mode liquid crystal display elements arerepresentatives of liquid crystal display elements of horizontalelectric field modes in which the liquid crystal alignment is horizontalto substrates in the voltage free state. These elements are particularlyexcellent in wide viewing angle performance. Still, no liquid crystaldisplay element is satisfactory in terms of all of the wide viewingangle performance, high contract performance, and high response speedperformance, whereby various improvements have been made in order toachieve satisfactory levels of all these performances.

For example, a liquid crystal device that includes liquid crystal havingnegative dielectric constant anisotropy sandwiched between a pair ofsubstrates is disclosed wherein at least one of the substrates includespixel electrodes and an inorganic alignment film for controlling thealignment of the liquid crystal on the pixel electrodes, and theinorganic alignment film includes a first oblique vapor deposition filmand a second oblique vapor deposition film each of which is formed byperforming oblique vapor deposition on the substrate from an oppositedeposition (for example, Patent Document 1). Another example is a liquidcrystal device including an alignment film of a porous inorganic film onat least one of a pair of substrates wherein the alignment film includesa plurality of convex portions on the surface facing a liquid crystallayer, and the convex portions each have a long axis and a short axiswhen viewed in a plan view (for example, Patent Document 2). Stillanother example is an active matrix liquid crystal display devicewherein the extrapolation length, which indicates the strength oftwisted bonds between liquid crystal molecules at the interface betweenan alignment film and a liquid crystal layer, and the alignment filmsurface, is not less than 10% of the gap between a pair of substrates(for example, Patent Document 3). In addition, TBA mode liquid crystaldisplay devices and the like have also been disclosed (for example,Patent Documents 4 to 10).

PRIOR ART REFERENCES Patent Documents

Patent Document 1: JP 2008-225032 A

Patent Document 2: JP 2008-191264 A

Patent Document 3: JP 2005-189889 A

Patent Document 4: JP 57-618 A

Patent Document 5: JP 10-186351 A

Patent Document 6: JP 10-333171 A

Patent Document 7: JP 11-24068 A

Patent Document 8: JP 2000-275682 A

Patent Document 9: JP 2002-55357 A

Patent Document 10: JP 2001-159759 A

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

Regarding such liquid crystal devices as described above, limitation ofthe dielectric constant of the alignment films is not suggested. Inaddition, voltage reducing effects and high-speed response effects ofthese liquid crystal devices are not recited.

Regarding the above-described liquid crystal devices including liquidcrystal having negative dielectric constant anisotropy and an inorganicalignment film, more sufficient throughput (productivity) and easiercontrol of the tilt direction of liquid crystal molecules have beendesired.

The present invention has been made in view of the above problems and anobject of the present invention is to provide a liquid crystal displayelement that has sufficiently improved reliability and opticalcharacteristics and can be driven by a low voltage.

Means for Solving the Problems

The following describes how the present inventors have made the presentinvention with reference to an example of a TBA mode. However, thepresent invention is not limited to the TBA mode.

The present inventors have examined various ways to reduce the drivingvoltage of high-contrast liquid crystal display elements, and focused onthe movement of liquid crystal molecules caused by a voltage applied inthe TBA display mode in which the liquid crystal molecules are tiltedtoward the centers of non-electrode portions from their initial verticalalignment when an electric field is applied.

In the case of a TBA mode liquid crystal display element, liquid crystalshould be a material having a dielectric constant anisotropy Δε(hereinafter, also simply referred to as Δε of approximately 20 to bedriven (approximately −3 for the MVA mode and approximately 5 for the TNmode) if a voltage to drive the liquid crystal is set to be equivalentto those used in MVA and TN modes. Generally, materials having a largerΔε tend to have lower reliability and lower optical characteristics.

FIG. 7 shows data of the dielectric constant anisotropy Δε versus thetransmittance of liquid crystal materials used in a TBA mode including acommon organic alignment film (dielectric constant ε: 3, film thickness:1000 Å), which was obtained by applying 2 V, 3 V, and 4 V.

In order to achieve a desired transmittance using liquid crystal havinga Δε as small as possible, a high voltage should be applied. Thistendency is more apparent in the range over a certain Δε of liquidcrystal (Δε is approximately 10 or larger in the case of 2 V, which is astart-up voltage).

The reason why the driving voltage increases as described above is asfollow. In the case of the TBA mode, since the transmittance depends onliquid crystal in non-electrode portions, the non-electrode portions aredesigned to be as large as possible, which results in a larger distancebetween electrodes. For example, in the case of the MVA mode or the TNmode, the distance between electrodes (i.e. cell thickness) is typically3 to 4 μm. On the other hand, in the case of the TBA mode, the distanceis approximately 8 μm. Therefore, the threshold voltage should be high.In addition, in the TBA mode, since a pair of comb-shaped electrodes fordriving liquid crystal molecules located therebetween is formed on oneof a pair of substrates, the electric field becomes weaker as it becomescloser to the substrate opposed to the comb-shaped electrode substrate.The movement of liquid crystal molecules likewise becomes weaker (thereexists a dead zone.) In order to avoid this, the threshold voltageshould be high.

As a result of intensive studies, the present inventors have found thata sufficient increase of an electric field applied to liquid crystal,which can be achieved by an alignment film having a higher dielectricconstant, and a reduction of the anchoring force (anchoring energy) inthe polar angle direction at the interface between a substrate and aliquid crystal layer are effective in sufficiently reducing the Δε ofthe liquid crystal and therefore achieving improved reliability andimproved optical characteristics, and also effective in reducing thedriving voltage.

Further, the present inventors have examined various practical methodsfor sufficiently enhancing the reliability and optical characteristicsand reducing the driving voltage of liquid crystal display elements ofTBA and other modes, and found that the electric field applied to liquidcrystal can be sufficiently increased, the Δε of the liquid crystal canbe sufficiently reduced, and the anchoring energy in the polar directionat the interface between a substrate and a liquid crystal layer can beeffectively reduced by forming an inorganic alignment film made of aninorganic material as a vertical alignment film of the substrate. Thepresent inventors thus found a way to solve the above problem andcompleted the present invention.

Specifically, the present invention provides a liquid crystal displayelement including: a pair of substrates; and a liquid crystal layersealed between the substrates, wherein the liquid crystal layer includesliquid crystal molecules having positive dielectric constant anisotropy,at least one of the substrates includes a pair of comb-shapedelectrodes, at least one of the substrates includes a vertical alignmentfilm in a display region on a face in contact with the liquid crystallayer, and the vertical alignment film is an inorganic alignment filmmade of an inorganic material.

The following discussion gives a detailed description of the liquidcrystal display element of the present invention.

The liquid crystal display element of the present invention includes apair of substrates and a liquid crystal layer sealed between thesubstrates. The liquid crystal layer is filled with liquid crystalmolecules that are aligned by applying a certain voltage. One or both ofthe substrates include lines, electrodes, semiconductor elements, andother components. Hence, the alignment of the liquid crystal moleculescan be controlled by applying a voltage.

In the liquid crystal display element of the present invention, theliquid crystal molecules are liquid crystal molecules having positivedielectric constant anisotropy (nematic liquid crystal molecules).Hence, the liquid crystal molecules are aligned along the direction ofan electric field when a voltage is applied to the liquid crystal layer.The liquid crystal molecules are, for example, aligned in arches. As aresult, a wide view angle can be achieved owing to self-compensation.

The dielectric constant anisotropy Δε of the liquid crystal molecules ispreferably not less than 10. In this case, the effects of the presentinvention can be more strongly exerted. The Δε is more preferably notless than 15. The upper limit thereof is preferably 25.

In the liquid crystal display element of the present invention, at leastone of the substrates includes a pair of comb-shaped electrodes. Theentire structure of the comb-shaped electrodes is not particularlylimited, provided that they include a comb's backbone and teethprojecting from the backbone when viewed in a plane view. In the casethat, for example, one of the comb-shaped electrodes is pixel electrodesprovided in respective pixels to receive a signal voltage and the otheris a common electrode to receive a constant common voltage, electricfields (for example, horizontal electric fields) can be formed in therespective pixels according to image signals transmitted to therespective pixel electrodes.

Preferably, the electrode distance between the comb-shaped electrodesis, for example, 7 to 9 μm.

At least one of the substrates includes a vertical alignment film on aface in contact with the liquid crystal layer, and the verticalalignment film is an inorganic alignment film made of an inorganicmaterial. The inorganic alignment film is preferably configured to alignthe liquid crystal molecules substantially vertically to a surface of atleast one of the substrates when no voltage is applied. In other words,the inorganic alignment film is preferably an inorganic alignment filmthat maintains the liquid crystal molecules near the surface at anangle, as determined assuming that the direction parallel to thesubstrate surface is 0°, of approximately 90° (90°±0 to 4°) toward thepolar angle direction, when no voltage is applied. The alignment may beattributed to the material of the inorganic alignment film or to thestructure of the inorganic alignment film.

The inorganic alignment film is preferably formed to cover the entiredisplay region when viewed along the normal to the substrate surface.

The structure of the liquid crystal display element of the presentinvention is not particularly limited by other components, provided thatit essentially includes the above-mentioned components.

The following gives a detailed explanation of preferred embodiments ofthe liquid crystal display element of the present invention.

In one preferred embodiment of the liquid crystal display element of thepresent invention, the inorganic material has a dielectric constant of 4to 6. In this case, a sufficiently large electric field can be appliedto the liquid crystal. Hence, a desired transmittance can be achievedeven if liquid crystal having a small dielectric constant anisotropy Δεis used to provide sufficiently improved reliability and opticalcharacteristics of the material and the threshold voltage is low (seeFIG. 7 and FIG. 8, which is a partially enlarged graph of FIG. 7).Typically, inorganic silicon materials have a dielectric constant of 6or less. An embodiment in which the inorganic material contains siliconis also one preferred embodiment of the present invention. It should benoted that the term “transmittance” in FIGS. 7 and 8 refers to atransmittance ratio determined by defining the transmittance 100% as 1.

The inorganic alignment film is preferably made of a material having aSiO bond. The use of a material having a SiO bond leads to a reductionof the anchoring energy to the liquid crystal molecules.

In another preferred embodiment of the liquid crystal display element ofthe present invention, the inorganic alignment film is provided only onthe at least one of the substrates which includes the comb-shapedelectrodes. In this case, the response performance of the liquid crystalmolecules is very good.

In still another preferred embodiment of the liquid crystal displayelement of the present invention, the inorganic alignment film is formedby printing, spin coating, or ink jetting. Hence, the liquid crystaldisplay element of the present invention can be easily formed, therebysufficiently improving throughput. The printing, spin coating, or inkjetting can provide an inorganic alignment film that aligns the liquidcrystal molecules vertically when no voltage is applied.

Any of the structures of the above embodiments may be combined withinthe scope of the present invention.

Effects of the Invention

The present invention enables an initial vertical alignment liquidcrystal display element to achieve improved reliability and improvedoptical characteristics of liquid crystal by using liquid crystal havinga small dielectric constant anisotropy Δε as a material and to bedriving by a low voltage.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view schematically illustrating a liquid crystaldisplay element of the embodiment 1 of the present invention;

FIG. 2 is a cross-sectional view schematically illustrating the liquidcrystal display element of the embodiment 1 of the present invention;

FIG. 3 is a graph of the voltage-transmittance property of TBA modecells of Examples 1 and 2 and Comparative Example 1 in the case that thedielectric constant anisotropy Δε of liquid crystal is 10;

FIG. 4 is a graph of the voltage-transmittance property of the TBA modecells of Examples 1 and 2 and Comparative Example 1 in the case that thedielectric constant anisotropy Δε of the liquid crystal is 15;

FIG. 5 is a graph of the voltage-transmittance property of the TBA modecells of Examples 1 and 2 and Comparative Example 1 in the case that thedielectric constant anisotropy Δε of the liquid crystal is 20;

FIG. 6 is a graph of the voltage-transmittance property of the TBA modecells of Examples 1 and 2 and Comparative Example 1 in the case that thedielectric constant anisotropy Δε of the liquid crystal is 25;

FIG. 7 is a graph of the dielectric constant anisotropy-transmittanceproperty of liquid crystal in TBA mode cells;

FIG. 8 is a partially enlarged graph of FIG. 7; and

FIG. 9 is a cross-sectional view schematically illustrating thestructure of a liquid crystal display element of the embodiment 2.

MODES FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention is described in more detail by way ofembodiments, but these embodiments are not intended to limit the presentinvention.

Embodiment 1

FIG. 1 is a perspective view schematically illustrating a liquid crystaldisplay element of the embodiment 1 of the present invention.

FIG. 2 is a cross-sectional view schematically illustrating the liquidcrystal display element of the embodiment 1 of the present invention.

As illustrated in FIGS. 1 and 2, the liquid crystal display element ofthe embodiment 1 of the present invention includes an array substrate101, an opposed substrate 111 facing a glass substrate 102, and a liquidcrystal layer 121 sandwiched between the array substrate 101 and theopposed substrate 111. The array substrate 101 includes a pair ofcomb-shaped electrodes 103 for generating a horizontal electric field,and is mainly constituted by the glass substrate 102 on which analignment film B having a vertical alignment group is disposed. Theopposed substrate 111 is mainly constituted by a glass substrate 112 onwhich a color filter (CF) 113 and an alignment film A having a verticalalignment group are disposed.

One of the comb-shaped electrodes 103 is pixel electrodes and the otheris a common electrode. Both of them basically include teeth. The teethof the pixel electrodes and the teeth of the common electrode areparallel to each other and the teeth of one of the comb-shapedelectrodes run into the gaps between the teeth of the other electrodewith a certain distance between each pair of adjacent teeth. The pixelelectrode refers to electrodes disposed in the respective pixels in thedisplay region and each of them receives an image signal. The commonelectrode is an electrode that is entirely conductive even on theboundaries of the pixels and receives a common signal.

When a predetermined voltage is applied to the comb-shaped electrodes103, an arch electric field is formed in the liquid crystal layer.Hence, positive nematic liquid crystal molecules (nematic liquid crystalhaving positive dielectric constant anisotropy) 122 are aligned into ahorizontal bend alignment along the applied electric field. The verticalalignment is maintained in portions overlapping the electrodes andportions overlapping the centers between pairs of the electrodes. Thus,liquid crystal molecules in the non-electrode portions contribute totransmission.

The liquid crystal display element of the embodiment 1 of the presentinvention is a TBA mode liquid crystal display element in which thepositive nematic liquid crystal (nematic liquid crystal having positivedielectric constant anisotropy) in the liquid crystal layer 121 isaligned vertically to the surface when no voltage is applied, and thealignment of the liquid crystal molecules in the liquid crystal layer121 is changed to a horizontal bend alignment by applying a horizontalelectric field (an electric field in the direction along the substrates)to the liquid crystal layer 121.

The transparent substrates 102 and 112 have polarizing plate 107 and108, respectively, on the surfaces opposite to the liquid crystal layer121. The liquid crystal display element of the present embodimentincludes a resin bead spacer for ensuring the liquid crystal layerthickness (cell gap) and a sealing material for sealing the liquidcrystal layer 121 between the array substrate 101 and the opposedsubstrate 111.

EXAMPLES 1, 2 AND COMPARATIVE EXAMPLE 1

As shown in Table 1, common organic matter has a dielectric constant ofapproximately 3 or less, and common inorganic matter has a dielectricconstant of approximately 4 or more. The term “ε_(Y)” refers to aspecific dielectric constant.

TABLE 1 Dielectric constant (∈_(γ)) Glass 5.4 to 9.9   Glass epoxysubstrate 4 to 4.8 Quartz 3.8 Rubber 2 to 3.5

FIGS. 3 to 6 show the voltage versus transmittance data (alignment filmthickness 1000 Å) of the TBA mode in which the dielectric constant ε ofthe alignment films A and B was 3, which corresponds to that of organicmatter, and 4 and 6 which correspond to that of inorganic matter(Comparative Example 1 and Examples 1 and 2, respectively) in the casethat the dielectric constant anisotropy Δε of liquid crystal was 10, 15,20, and 25.

FIG. 3 is a graph of the voltage-transmittance property of the TBA modecells of Examples 1 and 2 and Comparative Example 1 in the case that thedielectric constant anisotropy Δε of the liquid crystal is 10.

FIG. 4 is a graph of the voltage-transmittance property of the TBA modecells of Examples 1 and 2 and Comparative Example 1 in the case that thedielectric constant anisotropy Δε of the liquid crystal is 15.

FIG. 5 is a graph of the voltage-transmittance property of the TBA modecells of Examples 1 and 2 and Comparative Example 1 in the case that thedielectric constant anisotropy Δε of the liquid crystal is 20.

FIG. 6 is a graph of the voltage-transmittance property of the TBA modecells of Examples 1 and 2 and Comparative Example 1 in the case that thedielectric constant anisotropy Δε of the liquid crystal is 25.

In FIGS. 3 to 6, Δε is the dielectric constant anisotropy of the liquidcrystal, and ε is the dielectric constant of vertical alignment films.

FIGS. 3 to 6 demonstrate that an alignment film having a higherdielectric constant ε achieves a higher transmittance at low voltages.

The results can be summarized as follows.

(1) In the case that the Δε of liquid crystal is the same, an alignmentfilm having a larger ε allows start-up by a lower voltage or provides ahigher transmittance. Thus, the liquid crystal display element can bedriven by a low voltage.

(2) In the case of an alignment film having a larger ε, it is possibleto achieve a certain transmittance by a certain voltage even if theliquid crystal has a lower Δε. Therefore, liquid crystal having a lowerΔε can be used, resulting in improved reliability and improved opticalcharacteristics of the liquid crystal display element.

Tables 2 and 3 shows the results of physical property values in a commonMVA mode (vertical alignment) (three cases in which the ε of thealignment film is 3, 4, and 6 under the condition: Δε of the liquidcrystal=−3; and film thickness: 1000 Å) and the results of physicalproperty values in a common TBA mode (three cases in which the ε of thealignment film is 3, 4, and 6 under the condition: Δε of the liquidcrystal=20; and film thickness: 1000 Å) likewise in Examples 1 and 2 andComparative Example 1.

TABLE 2 Transmittance ratio in the case of 2.1 V application (star-upvoltage) Dielectric constant (∈) of alignment film 3 4 6 TBA (Δε = 20)100% 121% 154% MVA (Δε = −3) 100% 114% 130%

TABLE 3 Transmittance ratio in the case of 4 V application (grey levelvoltage) Dielectric constant (∈) of alignment film 3 4 6 TBA (Δε = 20)100% 105% 110% MVA (Δε = −3) 100% 103% 107%

The results shown in Tables 2 and 3 demonstrate that as the ε of thealignment film increases, the transmittance increases, and that thiseffect is more obvious in the TBA mode in which the Δε of the liquidcrystal is large. Thus, it is clear that the effect of the presentinvention is obvious in the TBA mode.

EXAMPLES 3-5 AND COMPARATIVE EXAMPLE 2

An alignment film having a SiO bond (SiOx (x=1 to 3)) and a verticalalignment group Y is provided as an inorganic alignment film 14 in eachof Examples 3 to 5. For example, an inorganic alignment film includingthe structure of the following formula (1) is preferably used. Thestructure of the formula (1) includes the vertical alignment group Y atthe terminal of a side chain of the main chain organosiloxane backbone.The structure of the formula (1) can be obtained by polycondensation ofalkoxysilan monomers.

(In the formula, l and m are the numbers of repetition of parenthesizedstructures and are positive integers.)

For example, Y is preferably a long chain alkyl group, a long chainfluoroalkyl group, a siloxane chain, or the like. In particular, Y ispreferably one of those represented by the formulas (2) to (8).

(In the formulas, X is a halogen atom, and is preferably fluorine.)

Examples of usable liquid crystal alignment agents include liquidcrystal alignment treatment agents disclosed in JP 9-230354A, liquidcrystal alignment treatment agents disclosed in WO 2003/042752, liquidcrystal alignment treatment agents for vertical alignment disclosed inWO 2005/052028, liquid crystal alignment agents for vertical alignmentdisclosed in WO2006/070819, and liquid crystal alignment agents forvertical alignment disclosed in JP 2006-30961 A.

The following gives a description of an actual procedure to produce aliquid crystal display element of Example 3 and the results ofevaluation compared to conventional liquid crystal display elements.Specifically, the liquid crystal display element of Example 3 wasproduced as follows.

First, a glass substrate for an array substrate was prepared. This glasssubstrate was provided with a pair of comb-shaped electrodes, which weretransparent electrodes of ITO (Indium Tin Oxide) or the like, on asurface. An inorganic solution for vertical alignment films containing acompound having the structure of the formula (1) was applied to theglass substrate and the comb-shaped electrodes by spin coating in such amanner to provide a film of 1000 Å after firing. Thereafter, thesubstrate coated with the solution was fired for about one hour at 200°C. In this manner, an inorganic alignment film was formed. The width ofeach tooth of the comb-shaped electrodes was 4.0 μm and the distancebetween the teeth was 8.0 μm (line/space=4.0 μm/8.0 μm).

Next, an inorganic alignment film was formed on a glass substrate for anopposed substrate by the same procedure. Subsequently, a resin beadspacer having a diameter to provide a desired cell thickness (d) wasdisposed on the array substrate, for example, by dispersion, and anepoxy sealing resin was printed on the opposed substrate. Thesesubstrates were then attached to each other, and the sealing resin wascured at 180° C. for two hours. In this manner, a liquid crystal cellwas produced.

Then, positive nematic liquid crystal (nematic liquid crystal havingpositive dielectric constant anisotropy) was sealed in the liquidcrystal cell by vacuum injection, and a polarizing plate was attached tothe surface of each glass substrate opposite to the liquid crystallayer. In this manner, the liquid crystal display element (Example 3)was produced. The Δn of the positive nematic liquid crystal (nematicliquid crystal having positive dielectric constant anisotropy) was suchthat a dΔn was approximately λ/2 by application of a voltage. The Δε ofthe liquid crystal was 22.

Finally, voltage-transmittance property data of the liquid crystaldisplay element of Example 3 was obtained by using a liquid crystalevaluation device LCD-5200 produced by Otsuka Electronics Co., Ltd.

Liquid crystal display elements were produced in the same manner as inExample 3, except that instead of the above-described inorganic solutionfor vertical alignment films, an organic alignment film SE-1211 freefrom SiO bonds (produced by Nissan Chemical Industries, Ltd.) was usedas a material for vertical alignment films to form the verticalalignment film A (Example 4), to form the vertical alignment film B(Example 5), or to form the vertical alignment films A and B(Comparative Example 1). Voltage-transmittance property data was alsoobtained in the same manner. The results obtained by the voltageapplication of (1) 0 V→6.5 V are shown in Table 4, and the resultsobtained by the voltage application of (2) 6.5 V→0 V are shown in Table5. Table 6 shows the total of the results of (1) and (2).

TABLE 4 (1) 0 V → 6.5 V Vertical alignment film A Inorganic OrganicVertical Inorganic 11.7 msec 11.8 msec alignment film B Organic 14.8msec 15.1 msec

TABLE 5 (2) 6.5 V → 0 V Vertical alignment film A Inorganic OrganicVertical Inorganic 6.8 msec 6.6 msec alignment film B Organic 6.7 msec6.4 msec

TABLE 6 (1) + (2) Vertical alignment film A Inorganic Organic VerticalInorganic 18.5 msec 18.4 msec alignment film B Organic 21.5 msec 21.5msec

(1) In the case that an inorganic alignment film is formed on thecomb-shaped electrode side (as the vertical alignment film B), theresponse speed to the voltage application of 0 V to 6.5 V is shorteneddue to weak anchoring of the inorganic film than that of an organic film(Table 4).

(2) Although the response speed to the voltage application of 6.5 V to 0V is generally slow in the case of weak anchoring, such delay of theresponse speed caused by weak anchoring hardly occurs because the bendalignment is changed to the original vertical alignment due to innerstress in this mode (Table 5).

The total response of (1) and (2) also demonstrates that the responsespeed is faster in the case that the inorganic alignment film is used onthe comb-shaped electrode side (as the vertical alignment film B).

These results demonstrate that the anchoring energy can be reduced byforming an inorganic alignment film on a substrate having a pair ofcomb-shaped electrodes, especially by forming an inorganic alignmentfilm only on a substrate having a pair of comb-shaped electrodes, whichleads to a threshold voltage reducing effect.

Although the inorganic alignment film is an inorganic alignment filmhaving a SiO bond and a vertical alignment group Y in the abovedescription, it is not limited only to such a film. Other examplesthereof include inorganic alignment films of AlOx, SiOx, TiOx, or SiC.Also, the inorganic alignment film in the present embodiment may be alaminate film of such an inorganic dielectric material as describedabove. These materials may be appropriately used together. The inorganicalignment film may further contain Al (aluminum), Ga (gallium), In(indium), Si (silicon), Ge (germanium), Sn (tin), Ti (titanium), Zr(zirconium), and/or Hf (hafnium). In this case, the anchoring energy canbe further reduced.

In the case that the liquid crystal display element of the presentembodiment further includes a driving circuit, a backlight (lightingequipment), and the like, it can be used in mobile phones, PDAs, carnavigation systems, PC monitors, televisions, and information displayssuch as guide boards in stations and outdoor notice boards.

Embodiment 2

A liquid crystal display element of the present embodiment differs fromthat of the embodiment 1 in the following respects. The liquid crystaldisplay element of the present embodiment includes an opposed electrodeon the opposed substrate side. Specifically, as shown in FIG. 9, anopposed electrode 61, a dielectric layer (insulating layer) 62, and avertical alignment film A are arranged in this order on the mainsurface, facing a liquid crystal layer 121, of a glass substrate 112. Acolor filter 113, a black matrix (BM), or the like may be providedbetween the opposed electrode 61 and the glass substrate 112.

The opposed electrode 61 is formed by a transparent conductive film madeof ITO, IZO, or the like. Both of the opposed electrode 61 and thedielectric layer 62 are formed to cover at least the entire displayregion without an exposed portion. A predetermined potential isuniformly applied to the entire opposed electrode 61 covering all thepixels.

The dielectric layer 62 is made of a transparent insulating material.Specifically, the dielectric layer 62 is formed by an inorganicinsulating film of silicon nitride, an organic insulating film of anacrylic resin, or the like.

Comb-shaped electrodes including pixel electrodes 20 and a commonelectrode 30, and a vertical alignment film B are provided on a glasssubstrate 102 like that of the embodiment 1. Polarizing plates 107 and108, respectively, are provided on the outer main surfaces of the twosubstrates 102 and 112.

Different voltages are applied between the pixel electrodes 20, and thecommon electrode 30 and between the pixel electrodes 20 and the opposedelectrode 61, respectively, for display except black display. The commonelectrode 30 and the opposed electrode 61 may be grounded. A voltage ofa certain magnitude and a certain polarity may be applied to both thecommon electrode 30 and the opposed electrode 61, or alternativelyvoltages of different magnitudes and different polarities may beapplied.

The liquid crystal display element of the embodiment 2 also sufficientlyimproves the reliability and the optical characteristics and can bedriven by a low voltage like that of the embodiment 1. In addition, theresponse speed is also improved since the opposed electrode 61 isformed.

Since the inorganic alignment films is remarkably fine, the use of aninorganic alignment film as the vertical alignment film A preventscomponents in the color filter 113 and the dielectric layer 62 frominvading the liquid crystal layer 121. Namely, the vertical alignmentfilm A serves as a barrier layer.

Also, the low-voltage driving and response speed increasing effect wereconfirmed in the embodiment 2 like in the embodiment 1.

Any of the structures of the above embodiments may be combined withinthe scope of the present invention.

The present application claims priority to Patent Application No.2010-006692 filed in Japan on Jan. 15, 2010 under the Paris Conventionand provisions of national law in a designated State, the entirecontents of which are hereby incorporated by reference.

Explanation of Symbols

-   20: Pixel electrode-   30: Common electrode-   61: Opposed electrode-   62: Dielectric layer-   101: Array substrate-   102, 112: Glass substrate-   103: Comb-shaped electrode-   107, 108: Polarizing plate-   111: Opposed substrate-   113: Color filter-   121: Liquid crystal layer-   122: Liquid crystal molecule aligned in bend alignment along applied    electric field-   123: Direction of applied electric field-   A, B: Vertical alignment film

1. A liquid crystal display element comprising: a pair of substrates;and a liquid crystal layer sealed between the substrates, wherein theliquid crystal layer comprises liquid crystal molecules having positivedielectric constant anisotropy, at least one of the substrates comprisesa pair of comb-shaped electrodes, at least one of the substratescomprises a vertical alignment film in a display region on a face incontact with the liquid crystal layer, and the vertical alignment filmis an inorganic alignment film made of an inorganic material.
 2. Theliquid crystal display element according to claim 1, wherein theinorganic material has a dielectric constant of 4 to
 6. 3. The liquidcrystal display element according to claim 1, wherein the inorganicalignment film is provided only on the at least one of the substratesthat comprises the comb-shaped electrodes.
 4. The liquid crystal displayelement according to claim 1, wherein the inorganic alignment film isformed by printing, spin coating, or ink jetting.